Looks like the Canadian version of GIRM 393

Likewise it is for the Conference to judge which musical forms, melodies, and musical instruments may be lawfully admitted into divine worship, insofar as these are truly suitable for sacred use, or can be made suitable.

differs considerably from the U.S. version

While the organ is to be accorded pride of place, other wind, stringed, or percussion instruments may be admitted into divine worship in the Dioceses of the United States of America, according to longstanding local usage, in so far as these are truly suitable for sacred use, or can be made suitable.

So I suppose in Canada you have to appeal to Sacrosanctum Concilium 120

In the Latin Church the pipe organ is to be held in high esteem, for it is the traditional musical instrument which adds a wonderful splendor to the Church's ceremonies and powerfully lifts up man's mind to God and to higher things.

But other instruments also may be admitted for use in divine worship, with the knowledge and consent of the competent territorial authority, as laid down in Art. 22, 52, 37, and 40. This may be done, however, only on condition that the instruments are suitable, or can be made suitable, for sacred use, accord with the dignity of the temple, and truly contribute to the edification of the faithful.

However, you're not going to find the prooftext you seek that says no pianos, only organ may be used. It just doesn't exist.

IF you're looking for a text which explicitly and exclusively applies to the Ordo of Paul VI, I'm afraid you're out of luck, because the modifiers will be shouted down: the piano isn't in accord with the dignity of temple, nor does it contribute to the edification of the faithful, but these concepts are simply taken as irrelevant in the modern environment. Look at any number of church buildings which aren't, themselves, in accord with the dignity of the temple action.

If the church has no organ, consider advocating for procuring a traditional pipe organ, rather than against piano. This isn't a hill to die on, in my opinion.

It would seem not, they only have “sentimental piano accompaniment”

I would consider first advocating for the music itself to be of a sacred quality. What comes to mind with the phrase “sentimental piano” is far from sacred. If the parish is accustomed to sentimental music and used to singing with the piano, suddenly changing both (or suddenly changing just one of these) can be jarring.

If chant and traditional hymnody take place of other “sentimental” musics, the piano accompaniment (or the accompanist!) will change by necessity. When sacred music is being sung well and established as the norm for the parish, it becomes clear that perhaps a pipe organ will be better suited than the percussive sound of a piano - no matter how beautifully played.

If all of this is handled well, with due patience and charity to the Aunt Betty’s who will miss “the good ol’ songs,” people will come to appreciate sacred music and be moved to prayer by it. On the other hand, if you put together an argument for organ vs. piano, no matter how legislatively sound your argument may be, and throw it down on the board room table in a sudden and sweeping decimation of all sentimental ditties, a lot of people are going to hate a lot of things, including you and your dreams of an organ. At that point sacred music has no chance of ever taking root (whether accompanied by piano or organ) and both sides will be embittered by the experience.

I know about those mixture III's and recently had a screaming one reduced in volume by about two thirds on my own organ. Years ago, when I played for college chapels, there was a Steinway 9 footer in the 1500 seat college church. It didn't have the volume or presence the pipe organ had and the consensus was it couldn't lead singing as well as the organ.

I tell folks wanting an organ about the clearing house where you can get a perfectly good organ for less than the cost of new. Also, I point to a local church on its 4th electronic while I am still playing our 1953 Schantz. A pipe organ can be repaired in 70 years. An electronic can not.

Ghmus,

Having worked in situations with most of the possible permutations, I'm convinced that if there isn't a functional organ and a competent organist, the best option all the way round is to have unaccompanied music.

Yea....where I work we have a Spanish choir with a number of guitars...however we also have a harpsichord and it is not allowed to be used in worship. Huh?

One might find success arguing this from the standpoint that the organ is better-suited to lead communal singing because its lack of decay and smooth onset is a closer match to the human voice.

A piano is a good contrast with the human voice—which is why piano-accompanied art songs work so well. But that assumes a solo voice and a situation where the voice is to be heard for its own merit; this is a very different context from worship.

Alas, though, most interested parties will approach ritual music the same way they approach listening to music on the radio, reducing all to a matter of individual taste. And on that field a lay musician cannot win on his/her own.

@ACabezon, I’m not sure where you are, but where I am (Mississauga) places that value sacred music are few and far between. I comfort myself with the sense that clergy in their 20s and 30s seem more amenable to it, so maybe about the time I retire (heh) things will improve.

It's adjacent to Toronto.

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I live within Mississauga as well, but most of my business in sacred music occurs in Toronto. The suburb is a bit of a liturgical no man's land.